Hi
Welcome to the forum.
Here is a video that will show you how to change the BPM/Tempo at any point in the song.
https://youtu.be/EXuZpg2UP9wBPM stands for "Beats Per Minuit." 60 BPM equals 60 beats per minute, for example.
Time signature defines how many particular note values are contained in each measure.
4/4 is one of the most common.
Simple time signatures consist of two numerals, one stacked above the other:
The lower numeral indicates the note value that the signature is counting. This number is always a power of 2, usually 2, 4, or 8.
The upper numeral indicates how many such note values constitute a bar. If this number is 2 or 4, the signature is described as duple meter; if 3, it is called triple meter. Other, less common, descriptors such as quintuple meter are occasionally used.
Try to stay with the most common time signatures until you get skilled in counting them. These common time signatures are 2/4, 4/4, and 3/4. Frequently used but less common are 6/8 and 12/8.
How to count the notes in a measure in 4/4 time. Turn on the metronome in Studio One. It is at the bottom on the right. There will be four clicks or sounds per measure.
Whole notes = 1 note per measure
Half notes = 2 notes per measure
Quater notes= 4 notes per measure
Eighth notes= 8 notes per measure
If you google this stuff you can find explanations that you can understand.
Hope this helps
Billy